The present invention relates to a fluorescent lamp, a method for manufacturing the fluorescent lamp and a fluorescent lamp device and preferably, to a fluorescent lamp which can cope with its lamp life end in a high frequency operation. More particularly, the present invention relates to a fluorescent lamp which can suppress melting of stem glass when inner lead wires of a stem are discharged as electrodes and can prevent short-circuiting between the inner lead wires caused by adhesion or deposition of spattering material produced by vaporization of filaments and inner lead wires, a method for manufacturing the fluorescent lamp and a fluorescent lamp device.
When a high frequency power is applied between counter electrodes of a fluorescent lamp to light the lamp, a phenomenon unique to lamp life (the lamp reaches its life end when the lamp has been operated for an accumulated time of several thousands of hours) end takes place. When the lamp comes to the end of the life and emitter material coated on filaments disappears, the lamp usually cannot come on and comes to its life end. However, even when the emitter of the filaments becomes null, there may occur such an unexpected situation that discharge is maintained with the filaments having the emitter already disappeared or inner lead wires being acting as hot spots. In this case, when discharge is maintained with, in particular, the inner lead wires acting as the hot spots, a discharge current larger than its rated value flows through the lead wires. For this reason, the lead wires may melt and eventually its stem may be thermally melted, which operation is called a first operation mode.
Further, in another life end mode of the fluorescent lamp, the material (W) of the filaments, the emitter material (BaO, etc.) coated on the filaments and the material (Ni, Fe) of the inner lead wires spatter and adhere or deposit onto tip end faces of flare stems close to the filaments. In particular, at the end of the lamp life, these substances tend to spatter and adhere or deposit onto the tip end face of each of the flare stems. The above adhesive or deposit, which is electrically conductive, may establish an electric path and energized when deposited. More specifically, the spattered material adhered and deposited on the tip end face of the flare stem may establish an electric path on the surface of the flare stem between a pair of electrically-isolated inner lead wires, thus leading to electric conduction between the inner lead wires. In such a case, a current flows through the electric path to heat the flare stem surface, which disadvantageously results in over-heat damage of the flare stem or in a large wattage loss due to short-circuiting. Such an operation mode is called a second operation mode.
The invention for overcoming the problem with the second operation mode is disclosed in JP-A-6-338289 Publication (referred to as the known citation 1, hereinafter), which will be briefly explained below.
FIGS. 1A to 1C shows an embodiment of a lamp disclosed in the known citation 1, wherein FIG. 1A is a cross-sectional view of the lamp, FIG. 1B is a cross-sectional view of the lamp taken along line Axe2x80x94A in FIG. 1A, and FIG. 1C is a cross-sectional view of the lamp taken along line Bxe2x80x94B in FIG. 1A. As shown in FIG. 1B, a recess 202 is made in a flare stem at at least one of root parts of a pair of inner lead wires 201 (The recess is made only at one lead wire in the drawing). In FIG. 1C, reference numeral 203 denotes an exhaust hole of an exhaust tube in the flare stem. Also disclosed in the citation 1 is that the recess may be made in an intermediate part 204 of the flare stem. Such a recess functions as a drop place. With such an arrangement, at the end of the lamp life, substance spattered from the electrode deposits on the flare stem. However, there is such a description in the citation that the presence of the recess functioning as the drop place makes it difficult for the substance to deposit only on that recess area, thus preventing establishment of an electric path and avoiding an electric short-circuiting between the pair of lead wires.
FIG. 2 is an alternate of the arrangement of FIG. 1 disclosed in the citation 1. In the drawing, the same reference numerals as those in FIG. 1 denote the same parts. The arrangement of FIG. 2 is different from that of FIG. 1 in that the recess 202 is replaced by such an insulation tube 205 as to surround the neighborhood of a sealing part of at least one of the inner lead wires 201 (The insulation tube 205 is provided only one lead wire in the drawing). With such an arrangement, the above spattered substance can deposit on the flare stem but less deposit on the inner lead wires 201 in the vicinity of the sealing part, thus blocking formation of the aforementioned electric path.
FIG. 3 shows another alternate of the arrangement of FIG. 1 disclosed in the citation 1. In the drawing, the same reference numerals as those in FIG. 1 denote the same parts as those in FIG. 1. A difference between the arrangement of FIG. 3 and that of FIG. 1 is that the recess 202 in FIG. 1 is replaced by an overhanging member 206 which is provided only for at least one of the pair of inner lead wires 201 (In the illustrated example, the overhanging member 206 is provided only one lead wire). There is such a description in the citation that, with such an arrangement, the aforementioned substance can deposit on the flare stem but the amount of substance deposited onto the inner lead wire 201 in the vicinity of the sealing part can be reduced, thus suppressing formation of the aforementioned electric path.
One of the related citations is JP-A-6-140000 Publication. The citation discloses an arrangement in which, as shown in FIG. 4, a glass bead 101 is fixedly mounted to a pair of lead wires 102. This enables reduction of an oxidizing rate of the lead wires and avoidance of an extremely short life of a fluorescent lamp. With such an arrangement, the presence of the glass bead 101 enables reduction of the amount of deposit spattered onto the lead wires 102 and onto an area 110 on the flare stem. However, since the above spattered deposit substance deposits on the glass bead 101, a short-circuiting may disadvantageously take place between the pair of lead wires through the deposit on the glass bead 101. In the drawing, reference numeral 105 denotes a bead mount, numeral 106 denotes a filament coil, 105 denotes a bead mount, 109 denotes an exhaust tube.
One of the related citations is JP-A-3-81950 Publication. The citation describes the aforementioned first operation mode. As an arrangement of overcoming the problem with the first operation mode, an arrangement of FIG. 23 is disclosed therein. FIG. 23 shows an arrangement in the vicinity of a lamp electrode. A button stem 27 is air-tightly joined to an end of a glass bulb 21 by means of an adhesive agent (not shown). Provided to the button stem 27 is a support rod 29, on which a heat shielding plate 30 is mounted. The heat shielding plate 30, which is disposed between an electrode 26 and stem 27, is made of heat-resistive metal such as stainless material. The heat shielding plate 30, which is shaped into a trough, covers a rear side of the electrode 26. Numerals 28a and 28b denote lead wires respectively. Such a description is disclosed in the citation that, with such an arrangement, even if the above first operation mode phenomenon takes place, the possibility of over-heat damage of the button stem 27 can be reduced because of the heat shield.
One of the related citations is JP-A-54-44372 Publication. The citation is directed to an improvement in an interior 2 of a fluorescent lamp 1, in which, as shown in FIG. 24, a circular heat shielding plate 13 is provided between a filament 12 and a base 9 to use the base 9 as a coolest point and to prevent heat radiated from the filament 12 from transmitting to the base 9. In this case, reference numeral 14 denotes lead wires, and numeral 15 denotes supporting members for supporting the heat shielding plate 13. This arrangement is intended to avoid deterioration of its good-looking lamp as a product caused by blackening of phosphor coated on a glass tube in the vicinity of the filament. To this end, the base 9 is set to have the coolest point to thereby suppress such blackening. With this arrangement, the shield is provided between the lead wire 14 and a stem 16, which is expected to suppress deposition of the above spattered substance onto the stem 16. However, this arrangement has a problem that, since the heat shielding plate 13 is fixed to the lead wire 14 without any substantial gap therebetween, the above spattered substance deposits on the heat shielding plate, thus disabling prevention of short-circuiting between the pair of lead wires 14.
The inventors of the present application have examined the fluorescent lamp disclosed in the above citation fluorescent lamp 1 and found several problems that the lamp cannot exhibit sufficient effects of reducing generation of the above first and second operation modes and cannot be easily manufactured on a mass production basis, etc.
(Problem with the First Operation Mode)
A problem common to the arrangements of FIGS. 1 to 3 is that no consideration is paid to avoiding the first operation mode in these arrangements. The first operation mode takes place for either one of the pair of lead wires, but in these arrangements, it is not clear that the first operation mode occurs in which lead wire. In order to properly cope with the first operation mode, it is necessary, even if the first operation mode takes place for either lead wire, to arrange the lamp in such a manner as to be able to cope with it. However, the citation fluorescent lamp 1 refers only to the fact that the recess, insulation tube and overhanging member are provided only for at least one of the lead wires in pair and fails to refer to the fact that they should be provided for both of the lead wires as its indispensable conditions. Such an arrangement cannot sufficiently cope with the first operation mode.
(Problems with the Second Operation Mode)
(1) With the arrangement of FIG. 1, since the creeping distance of the electric path is longer than that in the prior art, the probability of short-circuit occurrence is reduced to some extent. However, it is not necessarily sufficient and the electric path is established and short-circuited at a certain frequency. That is, as a result of examinations by the present inventors, it has been found that the second operation mode sometimes takes place.
(2) With the arrangement of FIG. 3, further, the overhanging member 206 is provided to the inner lead wire 201, which however is basically of a cantilever beam structure. Thus, as will be seen from FIG. 3, the substance deposits on the flare stem by going from the surrounding of the overhanging member, and the amount of such deposit becomes unneglibible. In other words, there cannot avoid eventual establishment of an electric path between the pair of lead wires.
(Other Problems)
(1) The arrangement of FIG. 2, there is described in the citation 1 that the insulation tube 205 may be made of ceramic, quartz or ordinary glass. In the case of using ceramic, however, the material of the flare stem is glass and thus a difference in thermal expansion coefficient between the ceramic and glass becomes large. Such a manufacturing step is employed that the lead wires are inserted into insulation tubes and then sealed with the flare stem of the glass material. In this case, because of the large difference in thermal expansion coefficient between the both materials, after the flare stem has sealed the insulation tubes, spontaneous cooling thereof involves a problem that the flare stem of glass is cracked. Further, when the insulation tube is made of glass, another problem is that the arrangement cannot sufficiently cope with the first operation mode. This is because generation of the first operation mode causes the lead wires to be heated, which disadvantageously melts the insulation tubes. In addition, even employment of any of the above materials inevitably involves complicated manufacturing steps.
(2) With the arrangement of FIG. 3, there is a description in the citation 1 that the overhanging member 206 may be made of ceramic, quartz, ordinary glass or metal. This arrangement requires the overhanging member 206 to be properly fixed to the lead wire. Otherwise, the overhanging member will be rotated about the lead wire and further moved along the lead wire, thus leading to deterioration of the original function of the member. In order to fix the both, further, some stoppers are necessary. The necessary number of such stoppers is 2 or 4. When the member is provided to one of the lead wires in pair, the total number of such stoppers is 2 because the electrode is provided at each of both ends of the discharge lamp. When the overhanging member is provided to each of the lead wires in pair, the number of such stoppers is 4 that is twice the above case. This involves a problem that member mounting works become troublesome and its manufacturing steps become complicated. An additional problem is that, when the overhanging member is made of glass material, the lamp cannot sufficiently cope with the first operation mode. This is because occurrence of the first operation mode causes heating of the lead wires to melt the member, with the result that the member eventually drops off from the wires.
It is therefore an object of the present invention to provide a fluorescent lamp which can overcome the above problems in the prior art, and also to provide a method for manufacturing the lamp.
The above object is attained by providing a fluorescent lamp employing any one of two first and second arrangements (1) and (2) which follow.
(1) First Arrangement
In a fluorescent lamp wherein a light emitting envelope is air-tightly sealed at each end with glass sealing material including a glass stem and a pair of first and second metallic lead wires, and a filament is provided to one ends of the pair of inner lead wires located inside the envelope; an insulator is provided between the filament and a top of the stem so that the first and second inner lead wires are passed through the stem and insulator, and the insulator covers boundary areas on the stem corresponding to the both lead wires or covers the entire top of the stem. In this case, the insulator is provided therein with first and second holes, into which the above lead wires in pair are inserted. A cross-sectional area of the holes is set to be larger than a cross-sectional area of the first and second lead wires. A value obtained by dividing the hole sectional area by the sectional area of the first and second lead wires is set to be not smaller than 1.2 and not larger than 10. Or a value obtained by dividing the diameter of the holes by the diameter of the first and second lead wires may be set to be not smaller than 1.1 and not larger than 3.3.
In this arrangement, there also be provided a fluorescent lamp which comprises a stem having the first and second lead wires for energization of an electrode and an electrically-insulating member provided therein with first and second holes, and wherein the first and second lead wires are inserted in the first and second holes so that a gap is defined between a boundary part of the first hole and the first lead wire in the vicinity of a contact part of the first hole with the first lead wire.
(2) Second Arrangement
In a fluorescent lamp which comprises a stem provided with first and second lead wires for energization of an electrode and electrically-insulating first and second members of a tubular shape having the first and second lead wires inserted therein, and wherein a cross-sectional area of the hollow part of the first and second members is larger than a cross-sectional area of the first and second lead wires. In this connection, a value obtained by dividing the cross-sectional area of the hollow part of the first and second members by the cross-sectional area of the first and second lead wires is set to be not smaller than 1.2 and not larger than 10. A value obtained by dividing a diameter of the hollow part of the first and second members by a diameter of the first and second lead wires may be set to be not smaller than 1.1 and not larger than 3.3.
In the first arrangement, since insulator is provided around the first and second lead wires, even when the first operation mode took place, advancement of abnormal discharge can be suppressed. Our experiments have showed that, when the first operation mode took place in a fluorescent lamp not having such an insulator, discharge causes lead wires to melt down to a flare stem level; whereas, when the first operation mode took place in a fluorescent lamp having such an insulator, the provision of the insulator enables such discharge to be suppressed or stopped. More specifically, it has been confirmed that the discharge was stopped with the lead wires remained on their filament side of the insulator.
With the arrangement, further, since the insulator is provided so as to cover the sealing boundary areas of the glass stem with the lead wires or to cover the entire head area of the stem, spattering of substance from the filament onto the flare stem or sealing areas can be more sufficiently suppressed than the prior art and thus a probability of generating the second operation mode can be reduced. Furthermore, since the insulator is provided therein with first and second holes or is structured as mentioned above, even the substance deposits on the insulator, the deposit will not lead to formation of a short-circuited path between the pair of lead wires. This is because gaps defined between the holes and lead wires act to block the formation of the short-circuited path.
Even in the second arrangement, since the first and second members are provided around the first and second lead wires, even when the first operation mode took place in either lead wire, the advancement of abnormal discharge can be suppressed. When the size of the hollow part of these members is selected sufficiently large when compared with the size or diameter of the lead wires, it has been confirmed that the provision of these members makes it difficult to maintain the above abnormal discharge. It has also been confirmed that, even when the discharge advances from the tip ends of the lead wires toward the flare stem, the provision of the members makes it difficult to maintain the discharge and the discharge stops short of reaching the members. It has also been confirmed that the absence of such members exhibits no such effect.
Further, since these tubular members cover the sealing areas and have an inner diameter sufficiently large when compared with the diameter of the lead wires, formation of a short-circuited path between the lead wires can be blocked.
The second arrangement is featured in that the first and second members having the hollow part sufficiently larger than the cross-sectional area of the lead wires are employed by design. This enables sufficient reduction of a short-circuit probability between the lead wires. Even with the arrangement of FIG. 2, it seems (not disclosed) that the inner diameter of the tube is slightly larger than the diameter of the lead wires, but a difference therebetween is such small as enough to tightly fit the both.